Acoustical panel



April 1963 R. E. JORDAN, JR., ETAL 3,084,402

ACOUSTICAL PANEL 2 Sheets-Sheet 1 Filed Nov. 1'7, 1958 mxxxm k 1 xxx,-

I INVENTOR.

Roy E. Jordan Jr. Howard 0. Maya BY Kim M. C/aus ATTORNEYJ A nl 9, 1963R. E. JORDAN, JR., ETAL 3,084,402

ACOUSTICAL PANEL.

Filed Nov. 17, 1958 2 Sheets-Sheet 2 INVENTOR.

BY Kar/ M Claus iv oofi o/ooo ooooyoo 0 0000000 0000000 0000000 00000000 OOOOOO 000000 000000 OOOOOO OOOOOO OOOOOOOOO OOGOOOOOOOO )0 OOOOO 0000o United States Patent s aman AcoUsrncaL PANEL Roy E. .lordan, l ra,Howard D. Mays, and Karl M. (Ilaus,

Zanesviile, @hio, assignors to The Miosalc Tile @ompany, Zanesville,Ohio, a corporation of ill-rib Filed Nov. 17, 1953, Ser. No. 774,177 13Claims. (ill. 2ll--4) This invention relates to acoustic insulating andabsorbing panel configurations for the reduction and control of airbornenoise.

The primary object of the invention is to provide a panel of materialhaving a finished surface of high decorative value and good soundabsorbing qualities and at the same time having an excellent acousticinsulating value, the panel being useful for any perimetrical enclosure,and being particularly advantageous for use in ceilings.

it is recognized that light weight, open materials, such as low densityglass fiber blankets or pads, can be made to act as very good soundabsorbers. The art has recognized that a material which may be a goodsound absorber may be, and usually is, a poor sound insulator. Porousmaterials or other types of sound absorbing treatment can reducesomewhat the level of noise after it is transmitted into a room; butthey do not provide the most effective means for preventing its initialentry.

It is also well known that noise originating in one room is transmittedto an adjoining room either through openings or by the diaphragmaticaction of the partition between the rooms. In modern buildings in whichthe partition between rooms may be movable, or temporary,

or of the non-load bearing type, the most importantpath of transmissionmay be over the top of the partition. The partition itself can becarefully designed against diaphragmatic action, the doors can betightly sealed and the fit of the partition to the floor and to thepermanent walls can be made acoustically tight to eliminate flankingpaths. The real problem thus narrows down to a consideration of thesound transmission properties of the ceilings in the room in which thenoise originates and the ceiling in the adjoining room to which itpropagates.

Modern structures of the non-load bearing wall or partition type usuallyutilize a dropped or false ceiling so that the space above it isavailable for ducts, pipes and conduits. A dropped or false ceilingcomprising merely a layer of acoustic absorbing material, such asacoustic tile, for example, is ineffective against the transmission ofnoise out of that room. While the room may itself be so quiet that anormal conversation can be carried on in it pleasantly, the conversationalso can be heard very readily in the next room. This is because thesound attenuation through the ceiling of the source room, along the openpath above the partition, and through the ceiling of the second ortermination room is very low.

in the consideration of the acoustic transmission prop erties of ceilingor wall panels it has been customary to consider any material which isacoustically transparent, such as the usual perforated facing board orpan, as making no significant contribution to acoustic insulation.Further, the transmission loss of a sound absorbing material is very lowand only increases directly in proportion to its thickness. For example,the transmission loss of rock wool having an apparent density of fivepounds per cuoic foot is about 2 db per inch of thickness at 500 cycles.in order to achieve a reasonable transmission loss, it would benecessary to employ an uneconomic and impractical thickness of wool, say16* inches or more. Thus a panel comprising the usual thin, acousticallytransparent, perforate facing backed by a layer of sound ice absorbingporous material would be expected to have, and does have, a very lowtransmission loss and is unsuitable for ceiling structures in buildingsof the type described above.

At most frequencies the transmission loss of a septum r diaphragmfollows the laws governing the transmis sion loss of a rigid wall orpartition. In this respect, then, according to present published data,the transmission loss of a septum or diaphragm would depend for allpractical purposes on its mass and would increase about 4-5 db for eachdoubling of the mass of the diaphragm or septum. Therefore, a thindiaphragm or septum would not be expected to add significantly to thetransmission loss of the panel at frequencies within the usuallyencountered range.

The present invention is based on the discovery that a panel having atransmission loss that is many times greater than would be expected froman analysis of the acoustic properties of its components can be made byproperly associating a relatively thin layer of sound absorbing materialand a thin, lightweight septum with a massive acoustically transparentbody. It has been found that the mass effect of the entire panel, andnot only the mass of non-porous elements, should be considered inarriving at the transmission loss of sound passing through it.

An obg'ect of the invention is to provide an acoustical panel having asone of its elements a massive facing material which has desirablephysical characteristics, such as ease of cleaning, color stability,controllable light reflectivity and the like and which panel has anexcellent sound transmission loss. All of these physical characteristicsrequired of the facing material are present in ceramic tile. Thus, thepresent invention provides a panel in which ceramic tile is preferablyused as a facing material, although a weighted or heavy metal sheet, adense heavy cernentitious material, or other similarly heavy material,may be alternatively employed.

Other objects and advantages of the invention will become apparent fromthe following specification, reference being had to the accompanyingdrawings, in which P16. 1 is a vertical sectional view through abuilding having a ceiling structure constructed in accordance with thepresent invention;

FIG. 2 is a fragmentary sectional view of a ceiling panel embodying apreferred form of the invention;

E16. 3 is a similar fragmentary, vertical sectional view of a ceilingpanel embodying a modified form of the invention;

FIG. 4 is an elevational view looking inwardly on the line 4- l of FIG.2;

P16. 5 is a view similar to H6. 4 but taken from the position indicatedby the line 5-5 of FIG. 3; and

FIG. 6 is a view similar to H6. 3 showing a ceiling panel embodyinganother modified form of the invention.

Referring to the drawings, and particularly to FIG. 1 thereof, thepresent invention is shown as embodied in a ceiling panel to reduce thesound transmission between rooms A and B. These rooms are separated by apartition C which is carried on a floor D. The roof of the building orthe floor above floor D is designated E. New ofiice buildings, schoolsand similar structures are now being constructed with what has becomeknown as a modular wall construction. In these buildings the walls arenon-load bearing and are built to touch a permanently installed butdropped ceiling and it is possible to rearrange the partitions or wallsbetween rooms in almost any desired manner. Space above the ceiling isprovided for electricity, heating and ventilating ducts, water conduitsand the like. At the present time the acoustical materials which areused in these ceilings do not adeacetates quately prevent the soundtransmission from one office space or room into the next.

In the drawings, the permanently installed ceiling is designatedgenerally 10 and this is suspended from the roof or upper floor by anysuitable means such as hangers 11 terminating in T-bars 12. Thus theceiling 10 cooperates with the roof or upper floor E to form a plenumspace 13 in which the conduits, pipes, etc., above mentioned, aredisposed. In most instances the plenum space 13 has a depth of at least10 which therefore forms an air space behind any acoustical ceiling thatmight be suspended from the hangers 11.

The preferred form of the invention is shown in somewhat larger scale inFIG. 2. As there indicated the ceiling panel 10 comprises a massivefacing layer 14, an intermediate fibrous sound absorbing layer 15adhered to the facing layer 14 by a layer of adhesive 16, and a septum17 adhered to the back of the fibrous mass 15 by a layer of adhesive 18.Each of the elements of the panel will be subsequently described in moredetail.

The facing layer 14, in the preferred form, comprises ceramic tilescemented or adhered together in side-toside relationship to form amassive continuous ceramic facing panel. The edge-to-edge cementing oradhesion of the tiles, indicated at 19 in FIG. 2, forms a unitarystructural body of any desired size. Any suitable cement may beemployed. For example, the tiles may be adhered by the use of a fritapplied thereto and subsequently fired or an organic cement such as anepoxy cement may be used. Such materials when properly applied will givea bond between adjacent tiles that is as strong as the tiles themselves.Thus 4 X 8 sheets of the ceramic tiles can easily be fabricated andutilized in the ceiling panels.

In a preferred form, each of the ceramic tiles is a modular 4 inchessquare, thick, and is perforated with A diameter holes on 7 centers.There are thus 81 holes per tile which results in about 14% open areawhich makes the tile acoustically transparent in the range offrequencies up to about 1000 cycles, with increasing refiection beyondthat frequency.

The open area of the tile could, of course, be achieved by utilizing anequivalent number and spacing of slots, if desired. Some enhancement ofthe absorptive effect of the blanket 15, hereinafter described, isobtained by the cylindrical perforations in the thick tile which resultin a dynamic resonator effect at frequencies in the range of 500 to 1000cycles since the hole depth is considerably greater than its diameter.

Ceramic tile is, of course, a massive material when utilized inthicknesses of /4 and over in that its weight per square foot is high.The Weight of the tile is about 2% lbs. per square foot. The thicknessused in the preferred form is substantially in excess of the thicknessof the tile that would be required merely for the structural support ofthe remainder of the elements of the panel. The ceramic tiles have, ofcourse, many other physical properties which ideally suit them for useas a ceiling material. The tiles are easy to clean, do not absorb odorsor moisure and do not require painting or other surface treatment.

Adhered to the rear surface of the massive facing layer 14, the presentinvention utilizes a sound absorbing blanket 15 which may be of anysuitable depth and density. The sound absorbing characteristics of theblanket can be changed in accordance with known criteria, and followvery closely the characteristics that would be expected from any blanketof the same material and thickness similarly mounted, except that thereis some enhancement due to the dynamic resonator effect of theperforated facing layer 14 at some frequencies. Measurements show thatthe blanket 15 is more effective when used with the facing layer of tilethan without at frequencies in the 500-1000 cycle range.

In the preferred embodiment of the invention the fid. brous layer 15comprises a glass fiber board having an apparent density of 6 lbs. percubic foot, and the layer is 1%" thick.

The sound absorbing layer 15, which is illustrated as fibrous, is aunitary, interstioed mass and is adhered to the facing layer and septumvas a unit possessing structural integrity in that adhesion of itssurface components, for example, the surface segments of the fibers, toeither the facing layer or the septum adheres the entire layer 15thereto. The preferred embodiment is glass fiber wool, densified bycompression and the fibers bonded together by a binder to form asubstantially stiff, at least semi-rigid, botardlike mass. The stiffnessof such sound absorbing materials, of course, depends upon theirthickness, constituents and density.

Continuously adhered to the rear face of the fibrous blanket 15, theseptum 17 may take sevenal different forms. It is only necessary thatthe septum be continuous in its area and that it be effectivelycontinuously adhered to the fibrous layer 15 which, in turn, is adheredto the facing layer 14. One form of septum that has been successfullyused comprises a As" sheet of compressed and bonded wood fibers such asis commercially kown as Masonite.

In a ceiling made up of a number of panels abutted against each other inedge t-o-edge relationship, it is prefenable to assure that there is noleakage path for sound through the edge of a panel or between the edgesof a panel and its supporting member. Closure of this edge leakage pathcan be readily accomplished by taping the exposed sides of the fibrousblanket 15 with an air impervious sheet material 20 such as cloth, metalfoil or plastic having an adhesive on one side. Further, the air leakagearound the taped panel may be reduced by using a compressible substancebetween the bot-tom. of the ceramic tile and the horizontal face of theT-bar, as indicated at 20a in FIG. 2. This will effectively prevent airleakage, and thus sound leak-age, past the sides of the panel into theplenum space .13.

A measurement of the sound absorption coefficient of the panel so fardescribed comprising the perforated ceramic massive facing layer, theadhered 1% glass fiber blanket and the adhered A3" Masonite septum showsthe following results:

Sound Absorption Opetiicient at frequency 0 While the sound absorptioncoefficient is not unexpected, it has been found that a panelconstructed in accordance with the invention shows a sound transmissionloss that is greatly in excess of the sound tnansmissi-on loss of itsvarious components. It will be appreciated, of course, that thetnansmissi-on loss of sound energy through the perforated ceramic tileis virtually zero. It is also understood that the transmission lossthrough the glass fiber blanket is also very low, being in theneighborhood of 2 db per inch of thickness. The transmission lossthrough the septum material above would also be very low, especially ifmetal foil or sheet plastic wereappear to have a very low transmissionloss, it has been found that when they are associated with each other inaccordance with the teachings of the present invention the transmissionloss of the panel is very high. Tests on a panel comprising I3. 4 footsquare specimen gave the following results:

Hour foot square specimen: Acoustic tile panels, 24" X 48", comprised of4 square Acoustic Wall Tile 7 thick, perforated with W d-ia. holes, 70.0., 81 per tile (14% open area), backed with 1% thick Fiberglas board,6 lbs/cu. ft. density and /s" tempered Masonite. Specimen comprised oftwo panels with joint simulating that of an exposed-T suspension system,outer periphery clamped in place without caulking.

llfid-frequency of warble-tone.

Differences between integrated sound pressure levels measured inreverberant source room and senii-anechoic ter rnination enclosure,determined in accordance with ASTM Standard E9055.

The attenuation of sound originating in room A would be expected toapproximate. 28 db before its entry into the plenum space 13. A similarattenuation would be expected between the plenum space and room B inconnection with the re-entry of the sound. Thus the attennation fromroom A to room B may be conservatively expected to exceed 40 db, and theacoustic insulation derived from the ceiling structure would thus equalor surpass the acoustic insulation derived from the partition betweenthe two noo-ms. At the present time partition manufacturers strive toachieve a 40 db transmission loss, and consider this to be acceptable.

To reduce the reverberation of sound in the plenum space after its entryinto that space from room A, for example, it may be desirable to add anacoustic absorbing material on the face of the roof or floor body E asindicated at 21 (FIG. 1). This will depend on the nature of theinstallation and such factors as the depth of the plenum space.

In order to prevent the transmission of sound longitudinally through thepanel a secondary septum extending at right angles to the facing layerand indicated at 22 in FIG. 1 should also be used. This septum 22 shouldbe located immediately over the partition C. The placing of thissecondary septum 22 requires only that a slot be made from the rear ofthe panel through the primary septum 117 and fibrous layer 15 and that apiece of Masonite or similar material be coated with an adhesivesubstance and forced into the slot. This will give ample adhesionbetween the secondary septum 22 and the fibrous layer 15.

FIGS. 3 and 5 show a modified form of the invention comprising a metalpan 30 having drawn or formed, inwardly extending cylindrical hollownipples 31 which correspond in form and effect to the perforations inthe tile of FIGS. 1 and 2. Additional mass can be imparted to the metalpan either by filling the space between the inwardly extending nipples31 with a heavy material such as plaster 32 or by increasing the gaugeof the metal of which the facing layer 30 is formed. The resultingfacing layer should have, for comparable results, substantially the samemass as the layer of ceramic tile 14 previously described.

FIG. 3 also shows the use of gasketing material 33 along the verticalleg of the T-bar suspension and adhered to the T-bar. This material 33is preferably put under compression by the setting of the ceiling panelsso that the possibility of transmitting sound through the space betweenthe T-bars and the panel is reduced to a minimum.

In the form shown in FIG. 3 the fibrous material 34 is adhered to thefacing layer 30 by a layer of adhesive 35 and a continuous septum 36 isprovided which is adhered to the back face of the fibrous material layer34 by a layer 37 of suitable adhesive. As in the case of the form shownin FIGS. 1 and 2, a secondary septum 38 over the partition should beemployed.

In the modification shown in FIG. 6, the septum is designated 39 andcomprises a layer of metal foil or a layer of plastic material. In thisform the metal foil or plastic sheet is overlapped from one panelsection to the next as shown at 46. This will also effectively preventtransmission of sound past the edges of the septum and into the plenumspace. As in the earlier embodiments, each panel comprises a layer offacing material 4 1 to which is continuously adhered a layer of fibrousmaterial 42 to which the septum 39 in continuously adhered. Adjacentpanels are similarly supported by T-bars 43.

As used herein and in the below claims, the term continuously adheredmeans that the adhesive employed contacts the surface of the facinglayer between the perforations and contacts the surface segments of thesound absorbing material and the adhesive which continuously adheres theseptum also contacts the surface segments of the sound absorbing layer,both adhesions extending over the entire areas involved.

An acoustical panel according to the invention as above describedpossesses the transmission loss characteristics of a rigid partition ofan equivalent or greater mass similarly jointed and at the same timepossesses accoustic absorbing properties equivalent to or greater than afibrous blanket of similar thickness. The usual rigid partition has ofcourse a very low noise reduction coefficient, and the usual fibrousblanket has, of course, a very low transmission loss.

What we claim is:

-1. An acoustical panel having a high transmission loss and high noisereduction coeflicient, said panel comprising, a perforate, substantiallysound transparent, facing layer, the perforations therein having a totalarea in excess of ten percent of the total area of said layer andconsisting of a rigid body having a mass per unit of area substantiallyin excess of that required for structural support of the remainder ofthe elements of the panel, a structurally integral layer of soundabsorbing material, a discrete thin layer of adhesive continuouslyadhering said layer of sound absorbing material to the back surface ofsaid facing layer, a continuous, air-impervious septum consisting of asheet of material having independent structural unity, and a discretethin layer of adhesive continuously adhering said septum to the backsurface of said sound absorbing layer.

2. An acoustical panel in accordance with claim 1 in which said soundabsorbing layer is fibrous material.

3. An acoustical panel in accordance with claim 1 in which said soundabsorbing layer is a board-like mass of densified intcrsticed glassfiber wool.

4. An acoustical panel in accordance with claim '1 in which said facinglayer consists of a sheet of perforated ceramic tile.

5. An acoustical panel in accordance with claim 1 in which said facinglayer consists of a massive sheet of perforated metal.

6. An acoustical panel in accordance with claim 1 in which said facinglayer consists of a sheet of cementitious material having independentstructural unity.

7. An acoustical panel in accordance with claim -1 in aosaaoa 7 whichsaid septum consists of an air impervious layer of compressed and bondedwood fibers.

8. An acoustical panel in accordance with claim 1 in which said septumconsists of a thin, air impervious flexible sheet metal.

9. An acoustical panel in accordance with claim 1 and a secondary airimpervious septum extending normal to the first said continuous septumthrough said layer of sound absorbing material.

10. An acoustical panel in accordance with claim 1 and an air impervioussheet material around the edges of said panel for preventing the leakageof sound there around and therethrough.

:11. An acoustical ceiling structure having a transmission loss inexcess of 20 db, and a noise reduction coefficient in excess of 0.70comprising a T-bar suspension system and acoustical panels supportedthereby, each of said panels comprising a perforate facing layer ofceramic tile, the perforations therein having a total area in excess often percent of the total area of said tile and a mass and rigiditysubstantially in excess of that required for structural support, saidfacing layer lying on the horizontal elements of the associated ones ofsaid T-bars and serving as the structural element of said panel, astructurally integral layer of sound absorbing fibrous material, adiscrete thin layer of adhesive continuously adhering said layer ofsound absorbing material to the back surface of said facing layer, acontinuous, air impervious septum consisting of a sheet of materialhaving independent structural unity, a discrete thin layer of adhesivecontinuously adhering said septum to the back surface of said layer ofsound absorbing material, and means at the edges of each of said panelsfor preventing the leakage of sound through said edges and between saidedges and said T-bars.

12. An acoustical panel having a high transmission loss and noisereduction coefiicient, said panel comprising, in combination, a facinglayer consisting of a sheet of substantially sound transparent,perforated, ceramic tile, the perforations therein having a total areain excess of ten percent of the total area of said layer and the sheetbeing rigid and having a mass substantially in excess of that requiredfor structural support, a layer of sound absorbing material consistingof a densified boardlike mass of intersticed glass fiber Wool, adiscrete thin layer of adhesive continuously adhering said soundabsorbing layer to the back surface of said facinglayer with theadhesive contacting the surface segments of said sound absorbingmaterial and the back face of said facing layer between the perforationsthereof, a continuous, air impervious septum and a discrete thin layerof adhesive continuously adhering said septum to the back surface ofsaid sound absorbing layer with the adhesive contacting the surfacesegments of the fibers thereof and the surface of said septum over theentire area involved, said septum being fabricated from independentlystructurally unitary material.

13. An acoustical panel according to claim 12 in which the septum is athin, lightweight, air impervious flexible sheet metal and the septumalso extends around the edges of at least the sound absorbing. layer andis ad hered to the surface segments of the fibers thereof.

References Cited in the file of this patent UNITED STATES. PATENTS.

1,910,628 Nash May 23, 1933 1,926,679 Kellogg et a1 Sept. 12, 19331,994,439 Slidell- Mar. 12, 1935 2,045,313 Roos et al June 23, 19362,077,713 Ross et a1 Apr. 20, 1937 2,132,032 lacobsen Oct. 4, 19382,177,393 Parkinson Oct. 24, 1939 2,200,382 Clarke May 14, 19402,350,513 Leadbetter June 6, 1944 2,450,911 Park et al Oct. 12, 19482,692,219 Slayter et al Oct. 19, 1954 2,767,440 Nelsson Oct. 23, 19562,779,979 Sundelin et a1. Feb. 5, 1957 2,802,764 Slayter et al. Aug. 13,1957 2,824,618 Hartsfield Feb. 25, 1958 2,829,790 Collings June 24, 1958FOREIGN PATENTS 588,498 Great Britain May 22, 1947 1,004,606 France Nov.28, 1951 524,931 Belgium Dec. 31, 1953

1. AN ACOUSTICAL PANEL HAVING A HIGH TRANSMISSION LOSS AND HIGH NOISEREDUCTION COEFFICIENT, SAID PANEL COMPRISING, A PERFORATE, SUBSTANTIALLYSOUND TRANSPARENT, FACING LAYER, THE PERFORATIONS THEREIN HAVING A TOTALAREA IN EXCESS OF TEN PERCENT OF THE TOTAL AREA OF SAID LAYER ANDCONSISTING OF A RIGID BODY HAVING A MASS PER UNIT OF AREA SUBSTANTIALLYIN EXCESS OF THAT REQUIRED FOR STRUCTURAL SUPPORT OF THE REMAINDER OFTHE ELEMENTS OF THE PANEL, A STRUCTURALLY INTEGRAL LAYER OF SOUNDABSORBING MATERIAL, A DISCRETE THIN LAYER OF ADHESIVE CONTINUOUSLYADHERING SAID LAYER OF SOUND ABSORBING MATERIAL TO THE BACK SURFACE OFSAID FACING LAYER, A CONTINUOUS, AIR-IMPERVIOUS SEPTUM CONSISTING OF ASHEET OF MATERIAL HAVING INDEPENDENT STRUCTURAL UNITY, AND A DISCRETETHIN LAYER OF ADHESIVE CONTINUOUSLY ADHERING SAID SEPTUM TO THE BACKSURFACE OF SAID SOUND ABSORBING LAYER.